In recent years there has been a growing interest in biological control of agricultural pests, i.e. by the use of microorganisms antagonistic to the pest, in view of the hazardous environmental effects of conventional chemical pesticides. Such a control has the advantage of being target specific and not polluting the environment.
PMD is a plant disease of world wide occurrence caused by various types of fungi which can infect many types of trees, flower plants, vegetables, fruit plants and various field crops, all of which will be referred to hereinafter collectively as "agricultural plants". A PMD infection is evidenced by a superficial, white or light grey powdery or felty growth on the surface of leaves, buds, young shoots, inflorescences, fruits and even flowers. In many cases the result of a PMD infection in agricultural plants is the reduction of the yields and quality of crop.
Up to date, no microorganisms which have the capability to combat PMD have been found. There has been a suggestion in the art (Wolf-Dieter Philipp and Gerd Cruger, Journal of Plant Diseases and Protection 86 (3/4), 129-142 (1979), to utilize a hyperparasite to the causative microorganisms of PMD, but all hyperparasites that have been isolated prior to the present invention, were found to have insufficient effectivity for the control of PMD in agricultural plants in the field in or in a greenhouse.
It is the object of the present invention to provide a pure culture of a hyperparasite of the causative microorganism of PMD, which may be utilised for controlling PMD.